Selank, Peptide Analogue of Tuftsin, Protects Against Ethanol-Induced Memory Impairment by Regulating of BDNF Content in the Hippocampus and Prefrontal Cortex in Rats.

The effects of a peptide anxiolytic Selank synthesized on the basis of the endogenous peptide tuftsin on memory impairment and content of brain-derived neurotrophic factor (BDNF) in brain structures were analyzed in outbred rats receiving 10% ethanol as the only source of fluid for 30 weeks. In the object recognition test, Selank (0.3 mg/kg a day, 7 days, intraperitoneally) produced a cognitive-stimulating effect in 9 months rats not exposed to ethanol (p<0.05) and prevented the formation of ethanol-induced memory and attention disturbances (p<0.01) developing during alcohol withdrawal. In ex vivo experiments, Selank prevented ethanol-induced increase in BDNF content in the hippocampus and frontal cortex (p<0.05). These results indicate positive effects of the tuftsin analogue on age-related memory disturbances associated with chronic alcohol intoxication and confirm the involvement of the neurotrophin mechanism related to BDNF production into the effect of Selank.

Treatment Effect of Tuftsin and Antigen Peptide Combined with Immune Cells on Colorectal Cancer.

BACKGROUND The aim of this study was to investigate the effect of antigenic peptides on dendritic cell maturation and activation as well as the role of dendritic cell induced cell function. The tumor-specific cytotoxic T lymphocytes induced by activation of the dendritic cells were also evaluated. MATERIAL AND METHODS SW-480 cell lysate and peptide antigens were selected as adjuvants in dendritic cell sensitization, and tuftsin was used to induce the phagocytosis of dendritic cells. Immature dendritic cells were stimulated with the antigen and adjuvant as follows: group A was negative control; group B was SW-480 (20 µg/mL); group C was SW-480 (20 µg/mL)+tumor necrosis factor (TNF)-alpha (10 µg/mL); group D was SW-480 (20 µg/mL)+tuftsin (20 µg/mL); group E was antigen peptide (2 µg/mL); group F was antigen peptide (2 µg/mL)+TNF-alpha (10 µg/mL); group G was antigen peptide (2 µg/mL)+tuftsin (20 µg/mL). Cytotoxic T lymphocytes activation and in vitro anti-tumor effects were examined by detecting the maturation marks of dendritic cells as well as interleukin (IL)-10 and IL-12 levels secreted by dendritic cells. Cells with the strongest immunizing effects were injected into nude mice and tumor suppression status was evaluated. RESULTS Group D (SW-480+tuftsin), group E (antigen peptides), group F (antigen peptide+TNF-alpha), and group G (antigen peptides+tuftsin) displayed significant differences compared to the control group (P<0.05). Group G (antigen peptides+tuftsin) could also promote the secretion of cytokines IL-12, as well as inhibit cytokine IL-10 secretion, compared to the other experimental groups (P<0.05). In the in vivo experiments of tumor inhibitions, antigenic polypeptide+tuftsin was the most effective (P<0.05). CONCLUSIONS Combination of cytotoxic T lymphocytes and T peptide therapy in treating human colorectal cancer might be used as a new treatment strategy based on adoptive cellular immunotherapy.

Chemical and biological properties of a supramolecular complex of tuftsin and cucurbit[7]uril.

Cucurbit[7]uril (CB7) is an uncharged and water-soluble macrocyclic host. CB7 binds to doubly protonated tuftsin, which is the tetrapeptide Thr-Lys-Pro-Arg, with moderate affinity (Ka=2.1×103M-1). In this study, the host-guest complexation was confirmed by fluorescence titration. This affinity would allow for easy release of the peptide under physiological conditions. According to density functional theory calculations, the structural binding motif involves hydrogen bonding. The most energetically stable form had the Arg side chain inside the CB7 cavity. The effects of the tuftsin-CB7 complex on the proliferation and cytokine activity of immune cells were studied. The complex had broader spectrum immunomodulation than free peptides, and caused statistically significant (p<0,05) changes in cytokine production (tumor necrosis factor-α, interleukin-2, interferon-γ, and interleukin-10) by mononuclear cells. By contrast, the free peptide only activated tumor necrosis factor-α production.

Tuftsin-driven experimental autoimmune encephalomyelitis recovery requires neuropilin-1.

Experimental autoimmune encephalomyelitis (EAE) is an animal model of demyelinating autoimmune disease, such as multiple sclerosis (MS), which is characterized by central nervous system white matter lesions, microglial activation, and peripheral T-cell infiltration secondary to blood-brain barrier disruption. We have previously shown that treatment with tuftsin, a tetrapeptide generated from IgG proteolysis, dramatically improves disease symptoms in EAE. Here, we report that microglial expression of Neuropilin-1 (Nrp1) is required for tuftsin-driven amelioration of EAE symptoms. Nrp1 ablation in microglia blocks microglial signaling and polarization to the anti-inflammatory M2 phenotype, and ablation in either the microglia or immunosuppressive regulatory T cells (Tregs) reduces extended functional contacts between them and Treg activation, implicating a role for microglia in the activation process, and more generally, how immune surveillance is conducted in the CNS. Taken together, our findings delineate the mechanistic action of tuftsin as a candidate therapeutic against immune-mediated demyelinating lesions.

The second life of antibodies.

Antibodies (immunoglobulins, Ig) are used by the immune system to identify and neutralize foreign objects and are responsible for antigen-binding and effector functions. Immunoglobulin G (IgG) is the major serum immunoglobulin of a healthy human (~75% of the total Ig fraction). The discovery in 1970 of the endogenous tetrapeptide tuftsin (Thr-Lys-Pro-Arg, fragment 289-292 of the C(H2)-domain of the heavy (H) chain of IgG), possessing both immunostimulatory and neurotrophic activities, was an impetus for the search for new biologically active peptides of immunoglobulin origin. As a result, fragments of the H-chain of IgG produced as a result of enzymatic cleavage of IgG within the antigen-antibody complex were discovered, synthesized, and studied. These fragments include rigin (341-344), immunorphin (364-373), immunocortin (11-20), and peptide p24 (335-358) and its fragments. In this review the properties of these peptides and their role in regulating the immune response are analyzed.

Tuftsin signals through its receptor neuropilin-1 via the transforming growth factor beta pathway.

Tuftsin (Thr-Lys-Pro-Arg) is a natural immunomodulating peptide found to stimulate phagocytosis in macrophages/microglia. Tuftsin binds to the receptor neuropilin-1 (Nrp1) on the surface of cells. Nrp1 is a single-pass transmembrane protein, but its intracellular C-terminal domain is too small to signal independently. Instead, it associates with a variety of coreceptors. Despite its long history, the pathway through which tuftsin signals has not been described. To investigate this question, we employed various inhibitors to Nrp1's coreceptors to determine which route is responsible for tuftsin signaling. We use the inhibitor EG00229, which prevents tuftsin binding to Nrp1 on the surface of microglia and reverses the anti-inflammatory M2 shift induced by tuftsin. Furthermore, we demonstrate that blockade of transforming growth factor beta (TGFß) signaling via TßR1 disrupts the M2 shift similar to EG00229. We report that tuftsin promotes Smad3 phosphorylation and reduces Akt phosphorylation. Taken together, our data show that tuftsin signals through Nrp1 and the canonical TGFß signaling pathway. Despite the 40-year history of the tetrapeptide tuftsin (TKPR), a macrophage and microglial activator, its mechanism of action has not been defined. Here, we report that the tuftsin-mediated anti-inflammatory M2 shift in microglia is caused specifically by tuftsin binding to the receptor neuropilin-1 (Nrp1) and signaling through TGFß receptor-1, a coreceptor of Nrp1. We further show that tuftsin signals via the canonical TGFß pathway and promotes TGFß release from target cells.

Tuftsin-modified alginate nanoparticles as a noncondensing macrophage-targeted DNA delivery system.

The main objective of this study was to evaluate macrophage-targeted alginate nanoparticles as a noncondensing gene delivery system for potential anti-inflammatory therapy. An external gelation method was employed to form plasmid DNA-encapsulated alginate nanoparticles. The nanoparticle surface was modified with a peptide sequence containing tuftsin (TKPR), and transfection efficiency was determined in J774A.1 macrophages. The effect of transfected mIL-10 in blocking expression of tumor necrosis factor-alpha (TNF-α) was evaluated in lipopolysaccharide (LPS)-stimulated cells. Scrambled peptide- and tuftsin-modified cross-linked alginate nanoparticles efficiently encapsulated plasmid DNA and protected against DNase I degradation. The transgene expression efficiencies, measured using GFP and mIL-10 expressing plasmid DNA, were highest with tuftsin-modified nanoparticles. Levels of TNF-α were significantly lower (p < 0.0001) in LPS-stimulated cells that were transfected with mIL-10 using alginate nanoparticles. The results of the study show that noncondensing alginate nanoparticles can efficiently deliver plasmid DNA, leading to sustained in vitro gene expression in macrophages.

Design, synthesis, and in vitro activity of novel drug delivery systems containing tuftsin derivatives and methotrexate.

During the past decade, biodegradable polymers or oligopeptides recognized by cell-surface receptors have been shown to increase drug specificity, lowering systemic drug toxicity in contrast to small-size fast-acting drugs. The goal of the present study was to develop anticancer bioconjugates based on chemotactic drug targeting (CDT). These constructs are composed of methotrexate (Mtx) attached to a tuftsin-like peptide carrier through an enzyme-labile pentapeptide spacer (GFLGC) and several copies of a chemotactic targeting moiety (H-TKPR, For-TKPR, H-TKPKG, and Ac-TKPKG). Carriers with targeting moieties in the branches were prepared by solid-phase synthesis using mixed Boc and Fmoc strategies. The drug molecule connected to an enzyme-labile spacer was attached to the branched oligopeptide in solution. In vitro chemotaxis, cellular uptake, and cytotoxicity assays were carried out on the MonoMac6 cell line. The most effective conjugates with H-TKPR or Ac-TKPKG targeting moieties in the branches, which have the most advantageous chemotactic properties, can be internalized rapidly, and these conjugates trigger higher toxic effect than the free drug (Mtx). The results suggest that our tuftsin-based drug delivery systems might be potential candidates for targeting cancer chemotherapy.

Modulation of microglial/macrophage activation by macrophage inhibitory factor (TKP) or tuftsin (TKPR) attenuates the disease course of experimental autoimmune encephalomyelitis.

BACKGROUND: Myelin Oligodendrocyte Glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is the most commonly used mouse model for multiple sclerosis (MS). During the of progression of EAE, microglia, the immunocompetent cells of the brain, become activated and accumulate around demyelinated lesions. Microglial activation is mediated by the extracellular protease tissue Plasminogen Activator (tPA), and mice lacking tPA display altered EAE progression. In this study, we have used pharmacological inhibitors and stimulators of microglial/macrophage activation to examine the temporal requirement for microglial activation in EAE progression and to determine whether such approaches might potentially be of therapeutic value. RESULTS: Intervention using the tripeptide macrophage/microglia inhibitory factor MIF (TKP) and the tetrapeptide macrophage/microglial stimulator tuftsin (TKPR) attenuated EAE symptoms and revealed that the timing of macrophage/microglial activation is critical for the clinical outcome of EAE. We show that the disease progression can potentially be manipulated favorably at early stages by altering the timing of microglial activation, which in turn alters the systemic immune response to favor upregulation of T helper cell 2 genes that promote recovery from EAE. CONCLUSION: Preventative and therapeutic modulation of macrophage/microglial activity significantly alters the outcome of EAE at symptomatic stages. Specific molecular targets have been identified that represent potential avenues of exploration for the treatment and prevention of MS.

Tuftsin augments antitumor efficacy of liposomized etoposide against fibrosarcoma in Swiss albino mice.

Anticancer drugs are generally plagued by toxic manifestations at doses necessary for control of various forms of cancer. Incorporating such drugs into liposomes not only reduces toxicity but also enhances the therapeutic index. Some antioxidants and potent immunomodulators have also been shown to impart significant antitumor activity presumably by nonspecific activation of the host immune system. In the present study, we evaluated augmentation of the antitumor activity of etoposide (ETP) by the immunomodulator tuftsin in Swiss albino mice with fibrosarcoma. The efficacies of the free form of ETP, liposomized ETP (Lip-ETP), and tuftsin-bearing liposomized ETP (Tuft-Lip-ETP) formulations were evaluated on the basis of tumor regression, effect on expression level of p53wt and p53mut, and survival of the treated animals. Tuft-Lip-ETP, when administered at a dosage of 10 mg/kg body weight/day for five days, significantly reduced tumor volume, delayed tumor growth, and also up-regulated the expression of p53wt. In contrast, although Lip-ETP delayed tumor growth, it did not decrease tumor size. The results of the present study suggest that tuftsin incorporation in drug-loaded liposomes is a promising treatment strategy for various forms of cancers, including fibrosarcoma.

Mass spectrometric identification of the trypsin cleavage pathway in lysyl-proline containing oligotuftsin peptides.

Trypsin cleaves specifically peptide bonds at the C-terminal side of lysine and arginine residues, except for -Arg-Pro- and -Lys-Pro- bonds which are normally resistant to proteolysis. Here we report evidence for a -Lys-Pro- tryptic cleavage in modified oligotuftsin derivatives, Ac-[TKPKG]4-NH2) (1), using high-resolution mass spectrometry and HPLC as primary methods for analysis of proteolytic reactions. The proteolytic susceptibility of -Lys-Pro- bonds was strongly dependent on flanking residues, and the flexibility of the peptide backbone might be a prerequisite for this unusual cleavage. While -Lys-Gly- bonds in 1 were rapidly cleaved, the modification of these Lys residues by the attachment of a ss-amyloid(4-10) epitope to yield -Lys(X)-Gly derivatives prevented cleavage of this bond, and provided trypsin cleavage of -Lys-Pro- bonds, the pathway of this degradation being independent on the type of Lys-N(epsilon)-side chains (acetyl group, amino acid, peptide). Substitution of the Lys residues by Ala at the P'2 positions decreased the tryptic cleavage, while replacement of the bulky side chain of Thr at the P2 positions strongly increased the cleavage of -Lys-Pro- bonds. Circular dichroism (CD) data of the modified oligotuftsin derivatives are in accord with enhanced flexibility of the peptide backbone, as a prerequisite for increased susceptibility to cleavage of -Lys-Pro- bonds. These results obtained of oligotuftsin derivatives might have implications for the proteolytic degradation of target peptides that require specific conformational preconditions.

Tuftsin binds neuropilin-1 through a sequence similar to that encoded by exon 8 of vascular endothelial growth factor.

Tuftsin, Thr-Lys-Pro-Arg (TKPR), is an immunostimulatory peptide with reported nervous system effects as well. We unexpectedly found that tuftsin and a higher affinity antagonist, TKPPR, bind selectively to neuropilin-1 and block vascular endothelial growth factor (VEGF) binding to that receptor. Dimeric and tetrameric forms of TKPPR had greatly increased affinity for neuropilin-1 based on competition binding experiments. On endothelial cells tetrameric TKPPR inhibited the VEGF(165)-induced autophosphorylation of vascular endothelial growth factor receptor-2 (VEGFR-2) even though it did not directly inhibit VEGF binding to VEGFR-2. Homology between exon 8 of VEGF and TKPPR suggests that the sequence coded for by exon 8 may stabilize VEGF binding to neuropilin-1 to facilitate signaling through VEGFR-2. Given the overlap between processes involving neuropilin-1 and tuftsin, we propose that at least some of the previously reported effects of tuftsin are mediated through neuropilin-1.

Effect of liver transplantation on tuftsin activity and phagocytic activity of neutrophil granulocytes in patients with liver cirrhosis.

BACKGROUND: Tuftsin activity (TA) is reduced in cirrhosis. This contributes to the defective phagocytic activity (PA) of neutrophil granulocytes and is related to the impairment of splenic function. Orthotopic liver transplantation (OLT) cures cirrhosis and might restore TA. This study was aimed at determining if OLT restores TA and PA. METHODS: We measured in 9 cirrhotic patients, before and after successful OLT, TA by a bioassay and PA by chemiluminescence in which neutrophils of the patient were tested with both autologous (PA1) and pooled sera from healthy subjects (PA2). Splenic function was assayed by the pitted red cell count. RESULTS: Before OLT, TA was reduced in 7 patients, and PA1 in all the patients. Pitted cell count was elevated in all the patients. After OLT (median 39 months; range 21-49), TA improved in all cases [median: from 8% (5-16%) to 20% (9-22%), p < 0.008], normalizing in 5 out of the 7 patients with low values. PA1 improved in all the patients [from 102 cpm (65-128 cpm) to 235 cpm (78-280 cpm), p < 0.008], normalizing in 5. Pitted red count decreased in 7 patients and normalized in 3 [from 3.3% (2.1-6.0%) to 2.4% (1.4-2.8%), p < 0.021]. Platelet count [from 55 x 10(3) (30-100) to 185 x 10(3) (93-286), p < 0.008] and leucocyte count [from 3.60 x 10(3) (1.81-5.23) to 5.53 x 10(3) (3.31-6.71), p < 0.008] also improved. CONCLUSIONS: OLT improves TA and PA of cirrhotic patients. This effect is associated with an improvement of both functional hyposplenism and haematological hypersplenism. The restoration of natural defences against infections may mitigate the adverse effect of immunosuppressive treatment.

Development of a fast kinetic method for the determination of carboxypeptidase U (TAFIa) using C-terminal arginine containing peptides as substrate.

Carboxypeptidase U (CPU, TAFIa) is a novel determinant of the fibrinolytic rate. It circulates in blood as an inactive zymogen, procarboxypeptidase U, which is activated during the process of coagulation and fibrinolysis. CPU has a very short half-life at 37 degrees C. Its intrinsic instability complicates the determination of kinetic parameters of different substrates using an endpoint method. We developed a fast kinetic assay for measuring continuously the release of the C-terminal arginine by CPU independent of the nature of the substrate peptide used, allowing us to perform substrate specificity studies of CPU. This method uses arginine kinase, pyruvate kinase, and lactate dehydrogenase as auxiliary enzymes. The CPU activities measured using this kinetic assay were in the range of 97-103% of those determined with our HPLC-assisted reference assay, and the obtained K(m) and k(cat) values for hippuryl-l-arginine and bradykinin were in good accordance with those described in the literature. As expected, no arginine cleaving was seen using dipeptides and peptide substrates with a proline in the penultimate position. The presented kinetic assay enables the fast screening of substrates with a C-terminal arginine and is a valuable new tool for the kinetic evaluation of both synthetic and physiological substrates of CPU.

Tuftsin-bearing liposomes as antibiotic carriers in treatment of macrophage infections.

Tuftsin is a tetrapeptide (Thr-Lys-Pro-Arg) that specifically binds monocytes, macrophages, and polymorphonuclear leukocytes and potentiates their natural killer activity against tumors and pathogens. The antimicrobial activity of this peptide is significantly increased by attaching at the C-terminus a fatty acyl residue through the ethylenediamine spacer arm. This activity is further augmented by incorporating the modified tuftsin in the liposomes. The tuftsin-bearing liposomes not only enhance the host's resistance against a variety of infections but also serve as useful vehicles for the site-specific delivery of drugs in a variety of macrophage-based infections, such as tuberculosis and leishmaniasis.

Increase in the immunogenicity of HIV peptide antigens by chemical linkage to polytuftsin (TKPR40).

The use of synthetic peptide antigens in human prophylaxis still suffers from the very important problem of finding suitable carriers devoid of side effects. A desirable carrier for use in humans would be poorly immunogenic by itself, yet it would enhance the immune response to the peptide antigen. In the study reported herein, we examined the role of polytuftsin (TKPR40), a synthetic polymer of the natural immunomodulator tuftsin, as a carrier for synthetic peptides of HIV derived from the gp41 and gp120 proteins. Chimeric immunogens were constructed by chemical linkage between synthetic peptides of HIV and polytuftsin. These were employed for immunization of mice of different MHC haplotypes, and the humoral and cellular immune responses developed against the peptides were assessed by measuring total IgG, IgG, subclasses, T-cell proliferation, and in vitro cytokine release. A significantly stronger immune response was observed in mice immunized with the peptide-polytuftsin conjugates than in mice receiving the peptide dimers (peptide-peptide). Peptide-polytuftsin conjugates induced IgG2a and IgG2b isotype switching after both primary and secondary immunization. In addition, there was a positive correlation between the amounts of cytokines and the shift in the IgG isotypes. These data suggest that the use of polytuftsin as a carrier may increase the immune response against poorly immunogenic synthetic peptides.

ADP-ribosylation of tuftsin suppresses its receptor-binding capacity and phagocytosis-stimulating activity to murine peritoneal macrophages.

Arginine-specific ADP-ribosyltransferase present in granules of chicken polymorphonuclear leukocytes (so-called heterophils) is released into the extracellular space by stimulus of calcium ionophore A23187 or opsonized zymosan [Terashima et al. (1996) J. Biochem. 120, 1209-1215]. In the present work, we examined extracellular targets of the released transferase and identified tuftsin, a phagocytosis-stimulating tetrapeptide derived from leukokinin, as a preferential substrate of the enzyme in chicken plasma. Specific binding of FITC-tuftsin to murine peritoneal macrophages, observed under a fluorescent microscope, was impaired by ADP-ribosylation of the labelled peptide. Phagocytic assay analyzed by flow cytometry revealed that ADP-ribosylation of tuftsin decreased its phagocytosis-stimulating activity towards the macrophages. Thus, the ADP-ribosylation of tuftsin apparently decreases its biological activity and ADP-ribosylation may possibly be involved in inflammatory processes through alterations in tuftsin activity.

Quantitative assessment of tuftsin receptor expression and second messenger during in vitro differentiation of peripheral blood derived monocytes of leprosy patients.

Tuftsin, a tetrapeptide (Thr-Lys-Pro-Arg) is known to potentiate the immunogenic activity of antigen-fed macrophages. The present study describes the mechanism of action of tuftsin in leprosy patients throughout the spectrum of the disease in vitro as a function of culture age in terms of (A) involvement of second messengers cAMP, cGMP and [Ca2+]i and (B) number of tuftsin binding sites/and their relative affinities on the monocytes/macrophages. There is apparently no direct involvement of either cAMP or cGMP while comparing the stimulated and unstimulated cultures during in vitro differentiation of monocytes (days 1, 3 and 7) or with the spectrum of the disease. Inhibition of superoxide anion release either by verapamil or with Quin 2 clearly demonstrated the involvement of [Ca2+]i as a second messenger during activation of monocytes/macrophages with tuftsin. Scatchard analysis of radiolabelled tuftsin binding data showed only one type of tuftsin receptor (low affinity) on BL/ LL monocytes/macrophages and normal and BT/TT cultures showed a gradual change in receptor number and affinities (low to high) with the maturation of monocytes to macrophages in contrast to BL/LL groups which displayed significantly less number of receptors. This study elicits a model which depicts that the biological responses/metabolic functions of early monocytes of normal and BT/TT gradually increase with the age of the culture till day 3 and tapers off thereafter in the older (day 7) cultures, whereas the monocytes/macrophages of BL/LL group are metabolically active only on day 1. The present study thereby implies that the clearance of leprosy bacilli from lepromatous leprosy lesions as a consequence of local or systemic immunotherapy (in the present study, the macrophage modulation by tuftsin) depends on the influx of new competent macrophages, rather than the local activation of resident lepromatous macrophages.

Peptide cytokines in CNS and the immune system.

This study describes the effects of cytokine peptides released into the supernatant during an early allogeneic reaction (AR) of mouse spleen lymphocytes or brain cortex cells which differ in their major histocompatibility complex (MHC). The peptides were isolated by ultrafiltration, liquid chromatography and HPLC. We found that both peptides stimulated the cell surface Na+,K+-ATPase and Ca2+-ATPase activities of quiescent spleen lymphocytes in vitro and mimicked early allogeneic cell interactions. Both brain and spleen AR peptides inhibited Concanavalin A-stimulated spleen lymphocyte proliferation, whereas 3H-TdR incorporation into DNA of the E7 neuroblastoma cell line was stimulated by these peptides. The peptide isolated from the supernatant of the allogeneic brain cell reaction inhibited phagocytosis in phorbol myristate-stimulated LA5-9/8 mouse macrophage cell line. Immunosuppressive activity of spleen AR peptide is supported by inhibition of spontaneous E rosette formation by lymphocytes. The immunosuppressive effect of isolated peptide cytokines on lectin-activated lymphocytes was comparable with the serum thymic factor (FTS, Lenfant et al. 1983). These changes demonstrate the pleiotropic cytokine actions mediated by plasma membrane of immune system and brain cells.

Polytuftsin: its possible effects and mechanism during macrophage activation.

Polytuftsin (PT) a 35-40 repeat unit of tuftsin (TKPR), when administered as a conjugate with the malarial peptide, ring-infected erythrocyte surface antigen (RESA), enhanced antigen-induced lymphoproliferation and antibody levels in mice as compared to RESA alone. This enhancement was unrelated to the H-2 background of the animals. The present study was undertaken with a view to understanding the mechanism(s) responsible for this immune enhancement. Peritoneal adherent cells (PAC) from H-2b and H-2d mice were incubated with RESA alone, PT-conjugated RESA, a physical mixture of RESA + PT and PT alone. They were subsequently evaluated for I-A expression using monoclonal antibodies and flow cytometry as well as cell-ELISA. Significant increase in I-A expression on PAC was observed in all 4 groups as compared to untreated cells. Whereas cells treated with PT-conjugated RESA showed highly significant increase in I-A (P < 0.001), the other groups showed moderate increase (P < 0.05). This enhancement was attributable to increase in the number of I-A-positive cells rather than I-A molecules per cell. Moreover, IL-1 release, as assayed by bioassay, was significantly higher in cells treated with conjugated RESA as compared to cells treated with RESA or PT alone (P < 0.05). Thus, it would appear that PT-conjugated RESA peptide of the malarial antigen selectively enhances major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APC) and may therefore improve immune functions by stimulating better antigen presentation and proliferation of T cells.